refrigeration gas or elec

Discussion in 'Multihulls' started by taezow, Sep 14, 2010.

  1. taezow
    Joined: Jul 2009
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    taezow Junior Member

  2. CDK
    Joined: Aug 2007
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    CDK retired engineer

    If the weather information I saw is correct (7 sun hours in September), a 50 watts panel is all you need.
    And of course a 100 Ah battery to bridge a number of consecutive cloudy days.
     
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  3. Richard Woods
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    Richard Woods Woods Designs

    We ran a small fridge/freezer on solar panels in the Bahamas for the last two winters on our outboard powered 34ft Romany.

    We started with 120W which was marginal.

    The second year we added a second 120W panel, giving 240W total and that was ample. We also ran computers, the lights, nav instruments etc.

    On my Eclipse I had 200W total which was just enough to run the boat, including a water cooled fridge/freezer, at least until we got to Panama when it couldn't really cope.

    But in northern waters and in just tropical (like the Bahamas) 200W is fine to run a boat

    Hope that helps

    Richard Woods of Woods Designs

    www.sailingcatamarans.com
     
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  4. catsketcher
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    catsketcher Senior Member

    Fridges are a curse in an outboard powered boat. You need heaps of solar panels because you can still get cloudy days. In the winter you have less sun and shorter days. In the summer you get stronger sun for longer. On our boat when we had enough panels for winter - 200 watts - we had leftover for summer. We even used to run the breadmaker (just the first stage that mixed the dough and rose the yeast) to regulate the batteries.

    Remember if the battery bank is 100 amp hours you can only pull 50 amps out of them before they need a charge. You can't pull lead acids down below 50% or you shorten their life.

    I am considering whether to put 200 watts of panels on the new cabin. With no targa I like the clean lines Kankama has. I really like the idea of a cheap petrol generator that only makes DC power. A small $200 generator from a large hardware store could have its AC generator ripped of and a truck alternator put in its place linked to the petrol motor. You could generate 40 amps easily (but be careful of cooking the batteries).

    I have lived for 5 years under panels with an outboard but I don't know whether I would bother for our next trip. Some panels sure (maybe 100 watts) but you need extra batteries and the weight of a mount if you go only solar so a generator can be a good option - just makes sure it puts out heaps of DC

    cheers

    Phil
     
  5. catsketcher
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    catsketcher Senior Member

    Woah - just had a look at that fridge - its a bad choice for a boat. You want to put in your own or get a top opening and much better insulated box. That one is going to suck the juice. If it runs half the time then it will pull 12 x 2.5 = 30 Amp hours. I reckon it could be on more.

    To get 30 AH out of a battery you have to put about 36 AH in. At 12 volts this is 432 watt hours every day including cloudy ones. You have to have enough in the tank for cloudy days and enough panels to put the juice in quickly. I would guess 200 watts would just do this and the rest of the boat but a better fridge would help a heap.

    cheers

    Phil
     
  6. CDK
    Joined: Aug 2007
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    CDK retired engineer

    No Catsketcher, the fridge is excellent. I've used a very similar one with just a single horizontally mounted 50 watts panel on 4 weeks holidays. It needs only 8-12 Amp hours per day, which is less than the panel provides on an average summer day.

    In fact I still use the same fridge in my boat, but now without a solar panel because I only make shorter trips since I'm retired and discovered that the fridge can run several days on a well charged 80 Ah battery.
     
  7. catsketcher
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    catsketcher Senior Member

    Okay - I am intrigued that the thin looking walls would work well and the front opening is usually a no no. I learn something new

    cheers

    Phil
     
  8. CDK
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    CDK retired engineer

    My big LG home fridge has a buzzer that tells you to close the door. Very useful because searching for something in a well stocked fridge takes longer than you think.
    Teazow's fridge doesn't need one, there's only place for a some beer cans plus two Coke bottles in the door.
     
  9. jonr
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    jonr Senior Member

    I understand that you can put in some type of phase change thermal storage - so that you chill it when the sun is shining and then it lasts through the night - ie, battery free operation. Sounds more efficient and more durable.

    Seems strange that they don't make upright style refrig/freezer combinations.

    Here is a kit if you want to make your own built-in super insulated freezer (consider using rigid foam and spray foam):

    http://www.thetford.com/HOME/Products/NorcoldRefrigeratorsHome/SCQT4407/tabid/202/Default.aspx
     
  10. taezow
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    taezow Junior Member

    Thanks for all the replies.

    A top load will not fit into my boat, but this little guy fits perfect. I will be able to add insulation all around the unit. It will not hold much, but still a big upgrade from an ice chest. My wife will probably fill it with cheese.

    I was thinking of going gas but sounds like this one will not be too bad on 12V.

    Thanks again

    Tae
     
  11. aussiebushman
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    aussiebushman Innovator

    No one has yet commented on your gas question. Bad idea - they need to remain relatively level to work.

    Re electrical, work out the power consumption based on an anticipated 50% cycling, so if it draws 6 amps (typical) then in 24 hours it will require 6 X 12= 24 amps of power (obviously dependent on ambient temperature and the actual current draw. The battery should never be flattened below 40% so you will need at least a 60 AH battery, even without using it for lights etc and in practice, 100AH is far more practical. Now you know how much power you need to replace every day on average and allowing for dull days and the relative inefficiency of solar cells, you are probably looking at 2 X 100 watt panels minimum. This is in line with Richard and Phil's estimates.

    Cheers

    Alan
     
  12. taezow
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    taezow Junior Member

    aussie

    This is a very small fridge only draws 2.5 amps at 12v
     
  13. catsketcher
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    catsketcher Senior Member

    Difference between liveaboards and short cruisers

    Taezow - Bushman, Richard and I all built boats to live on long term so we come to the fridge question from that view. The maths is pretty solid - if it is on half the time (which is a good point to start from) then you need 36 Amp hours put back in each day. No getting around that.

    From a long term cruiser perspective you need lots of capacity and gentle battery treatment. A short cruise will have you set off with a full battery you can work down over the cruise. So the panel can be smaller and the battery too. The battery won't last as long.

    I put a fridge unit into my icebox. If your icebox is half decent then this will be a better solution in terms of current draw and volume. BUT you have to do the work.

    cheers

    Phil
     
  14. taezow
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    taezow Junior Member

    I can get the same size in a gas. I would have to gimble it of turn it off when to sailing. This might be a better solution.
     

  15. aussiebushman
    Joined: Oct 2009
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    aussiebushman Innovator

    I think you misread my post. I said 6 amps - which is what my Engel 30 litre draws and in "average" temperatures it cycles at 50%

    I repeat what I said about gas - a bad idea

    Alan
     
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